RT Journal Article SR Electronic T1 BCR-ABL1 expression, RT-qPCR and treatment decisions in chronic myeloid leukaemia JF Journal of Clinical Pathology JO J Clin Pathol FD BMJ Publishing Group Ltd and Association of Clinical Pathologists SP 817 OP 821 DO 10.1136/jclinpath-2015-203538 VO 69 IS 9 A1 Susan Latham A1 Paul A Bartley A1 Bradley Budgen A1 David M Ross A1 Elizabeth Hughes A1 Susan Branford A1 Deborah White A1 Timothy P Hughes A1 Alexander A Morley YR 2016 UL http://jcp.bmj.com/content/69/9/817.abstract AB Aims RT-qPCR is used to quantify minimal residual disease (MRD) in chronic myeloid leukaemia (CML) in order to make decisions on treatment, but its results depend on the level of BCR-ABL1 expression as well as leukaemic cell number. The aims of the study were to quantify inter-individual differences in expression level, to determine the relationship between expression level and response to treatment, and to investigate the effect of expression level on interpretation of the RT-qPCR result.Methods BCR-ABL1 expression was studied in 248 samples from 65 patients with CML by determining the difference between MRD quantified by RT-qPCR and DNA-qPCR. The results were analysed statistically and by simple indicative modelling.Results Inter-individual levels of expression approximated a normal distribution with an SD of 0.36 log. Expression at diagnosis correlated with expression during treatment. Response to treatment, as measured by the number of leukaemic cells after 3, 6 or 12 months of treatment, was not related to the level of expression. Indicative modelling suggested that interpretation of RT-qPCR results in relation to treatment guidelines could be affected by variation in expression when MRD was around 10% at 3 months and by both expression variation and Poisson variation when MRD was around or below the limit of detection of RT-qPCR.Conclusions Variation between individuals in expression of BCR-ABL1 can materially affect interpretation of the RT-qPCR when this test is used to make decisions on treatment.